1. Field of the Invention
The present invention relates to a method and apparatus for manufacturing resins and resin compounds. More particularly, the invention relates to an apparatus and method for extruding resins and resin compounds through a die.
2. Description of the Prior Art
In the process of electrophotographic printing, a photoconductive surface has an electrostatic latent image recorded therein. Toner particles are attracted from carrier granules to the latent image to develop the latent image. Thereafter, the toner image is transferred from the photoconductive surface to a sheet and fused thereto.
Typically, toner may be produced by melt-mixing the polymer and pigment whereby the pigment is dispersed in the polymer. The polymer having the colorant dispersed therein is then pulverized. Recently in U.S. Pat. No. 5,227,460 (Mahabadi et al.), incorporated herein by reference, a low melt toner resin with minimum fix temperature and wide fusing latitude containing a linear portion and a cross-linked portion containing high density cross-linked microgel particles, but substantially no low density cross linked polymer was disclosed. A method of manufacturing that toner and its resin was disclosed in U.S. Pat. No. 5,376,494 (Mahabadi et al.), incorporated herein by reference. The method of fabricating the low fix temperature toner resins includes a reactive melt mixing process wherein polymer resins are cross-linked at high temperature and high shear. The resins are particularly suitable for high speed fusing, show excellent offset resistance and wide fusing latitude and superior vinyl offset properties.
The polymer and pigment are melt mixed together typically in an extruder which is part of an extruding system. The polymer and pigment are translated and mixed in an auger within a cavity of the extruder. A die plate is located on the exit end of the extruder. A conventional die plate has round holes to enable the extrusion of high viscosity materials and subsequent processing which includes thinning , cooling and crushing. A conventional strand die plate with small holes would be prone to plugging and would generate extremely high back pressure. This would result in vacuum vent flow and other processing problems that create considerable down time to the extruding machine.
Often, the die plate has to be removed from the extruder for off-line cleaning, which is a length and labor intensive activity. To avoid the plugging and time consuming off-line cleaning associated with the die plates with small holes, die plates with much larger holes have been used.
When large holes are used for the die plate, a large slab of high viscosity extrudate exits from the extruder. This extrudate must be squeezed and spread by nip rolls. This large high viscosity slab often slips when entering the nip rolls. Subsequent processing of this cross sectional slab is very difficult. The slab is typically much thinner at the outer edges of the slab making the processing even more difficult
The following disclosures may be relevant to various aspects of the present invention: